A "Qi" feeling (a kind of comfortable sense) during and after acupuncture is one of the important determinants to decide quantity (trial number) of acupuncture stimulation. It has been reported that various autonomic responses were evoked when patients felt "Qi" and when acupuncture stimulation had significant effects on EEGs. However, quantitative relationships among acupuncture stimulation, EEGs, and autonomic responses remain unclear. In the present study, autonomic functions [ECGs, heart rate (HR), blood pressure (BP)] and EEGs were analyzed during and after acupuncture stimulation. Acupuncture stimulation was given to the neck of the subjects. The subjects were required to push a button when they felt "Qi". The results indicated that acupuncture significantly decreased HR, and increased systolic BP (SBP). Spectral analysis indicated that acupuncture significantly decreased low frequency components (LF) of HR variability (HRV) and SBP variability (SBPV), and also significantly reduced ratio of LF to high frequency component (HF) of HRV (indices of sympathetic activity). Furthermore, there were significant negative correlation between changes in LF/HF ratio of HRV and number of acupuncture trials, and significant positive correlation between HF of HRV (index of parasympathetic activity) and number of acupuncture trials. Analyses of EEGs data indicated increases in all EEG bands during acupuncture. Furthermore, HF of HRV was positively correlated with power of all EEG bands, while LF of SBP and LF/HF of HRV were negatively correlated with these spectral data. These results suggest that physiological effects of acupuncture are mediated through the central nervous system.